An energy-efficient, dynamic voltage scaling neural stimulator for a proprioceptive prosthesis

Abstract

Abstract-This paper presents an 8 channel energy-efficient neural stimulator for generating charge-balanced asymmetric pulses. Power consumption is reduced by implementing a fullyintegrated DC-DC converter that uses a reconfigurable switched capacitor topology to provide 4 output voltages for Dynamic Voltage Scaling (DVS). DC conversion efficiencies of up to 82 % are achieved using integrated capacitances of under 1 nF and the DVS approach offers power savings of up to 50 % compared to the front end of a typical current controlled neural stimulator. A novel charge balancing method is implemented which has a low level of accuracy on a single pulse and a much higher accuracy over a series of pulses. The method used is robust to process and component variation and does not require any initial or ongoing calibration. Measured results indicate that the charge imbalance is typically between 0.05 % -0.15 % of charge injected for a series of pulses. Ex-vivo experiments demonstrate the viability in using this circuit for neural activation. The circuit has been implemented in a commercially-available 0.18 μm HV CMOS technology and occupies a core die area of approximately 2.8 mm 2 for an 8 channel implementation.

A power‐efficient current‐mode neural/muscular stimulator design for peripheral nerve prosthesis

“…It is known that the voltage-mode stimulation provides the highest PE 19,20 because ideally, V load equals to V stim at the output stage of the stimulator. [22][23][24] For PE of current-mode stimulator, also considering the output current branch as the output stage only, the PE is expressed as The charge-mode stimulation as shown in Figure 1C has accurate control over the amount of injected charge.…”

“…The above-mentioned deficiencies of voltage-mode and charge-mode stimulation methods make the current-mode stimulation the most widely adopted method in stimulator designs. [22][23][24] For PE of current-mode stimulator, also considering the output current branch as the output stage only, the PE is expressed as…”

Advances in Microelectronics for Implantable Medical Devices

“…(3) H-bridge with multiple current sinks [80]. This approach assumes an asymmetric biphasic waveform.…”

“…However, if the current sink that is active in the anodic phase is sequentially changed after each stimulus waveform, then after cycles each sink would have been active for the same amount of time during the cathodic and anodic phases, yielding accurate charge balance. The method is claimed to achieve a maximum charge mismatch of 0.45% [80].…”

Modelling muscle spindle dynamics for a proprioceptive prosthesis

“…a neural implant which would mimic the function of the human proprioceptive system in the same way a cochlear implant mimics the function of the human auditory system. A proprioceptive prosthesis is envisaged to broadly consist of 3 parts: (1) sensors fitted to a prosthetic limb to track its position, motion and the forces exerted on it; (2) processing that translates the sensor data into neural signal patterns that mimic those produced by proprioceptive receptors found in the human body; and (3) an implanted neural stimulator [3] to "transmit" these artificial neural patterns into the user's peripheral nervous Fig. 1.…”